Method of making insulating material and apparatus therefor



Sept. 29, 1936. J. F. PALMER 2,055,877

METHOD OF MAKING INSULATING MATERIAL AND APPARATUS THEREFOR Original Filed Nov. 25, 1932 3 Sheets-Sheet l I h gig/@912 151 Ila/27a Pa (722671 Wwy 1M4, L22? Sept. 29, 1936. J. F. PALMER 2,055,877

METHOD OF MAKING INSULATING MATERIAL AND APPARATUS THEREFOR Original Filed Nov. 25, 1932 3 Sheets-Sheet 2 41 720602??? Wan 277267 Sept. 29, 1936. J, PALMER 2,055,877

METHOD OF MAKING INSULATING MATERIAL AND APPARATUS THEREFOR Original Filed Nov. 25, 1932 3 Sheets-Sheet 3 A 1 15 4. I. W

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Patented Sept. 29,- 1936 UNITED} STATES METHOD OF MAKING INSULATII V G MATE- BIAL APPARATUS THEREFOR John F. Palmer, St. Joseph, Mich. Original application November 25, 1932, Serial .No, 644,195. Divided and this March 2, 1935, Serial No. 8,999

application 18 01am (Cl. 154-28) My invention relates to a method of making insulating material and to apparatus therefor. The insulating material to which my method and apparatus are particularly adapted is one comprising, in whole or in part, a pair of paper sheets, and especially where both the inner and outer surfaces of both sheets are coated with a water proofing material such as rubber latex, one of the sheets constituting a fiat backing sheet and the other sheet being corrugated and cross-corrugated to isolate a multiplicity of small air cells each of which is completely enveloped by a rubber lining which hermetically seals the air in the cell.

The objects of my invention; as regard the method and apparatus, include the following:

The formation of the primary corrugations in a sheet of paper without pressing the paper between intermeshing metal teeth, which might go tear or weaken the paper; the formation of secondary or cross-corrugation without further weakening the paper sheet; the application of a backing sheet to the corrugated sheet immediately upon the formation of the corrugations so that the feeding pull upon the corrugated sheet does not tend to pull out or flatten the corrugations; the corrugating of a sheet and adhering the corrugated sheet to a backing sheet, with a coating material applied to both surfaces of both sheets without bringing the corrugating or feeding rollers into contact with the sticky coating; and the formation of isolated cells with air under pressure permanently entrapped in the cells.

The fc iregoing, together with further objects, features and advantages of my invention, are set forth inthe following description of a specific embodiment thereof and illustrated in the accompanying drawings wherein: p

Figure 1 is a schematic perspective view of an apparatus for producing the insulating material of my invention;

Figure 2 is a fragmentary detailed section illustrating the apparatus for app ying suction to the corrugations of the corrugating roll to corrugated paper pneumatically;

Figure 3 is a perspective view of the corrugated side of a piece of a cellular sheet;

Figure 4 is a'plan view of the corrugated side of a small piece of multi-cellular sheet similar to that shown in Figure 3, the respective edges of the sheet having been "cut at various positions in respect to the corrugations; whereby the several edge elevations correspond to various sec- 'tiP-ns and the confusion of cross section lines in indicating typical cross sections is thus avoided;

Figure 5 is an edge elevation of the piece of Figure 4 looking along the line 5-5 of Figure 4 and simulating a cross section across the primary 5 or transverse corrugations and intermediate the secondary or longitudinal corrugations:

Figure 6 is an edge elevationof'the piece of Figure 4 looking along the line 6-6 of Figure 4 and simulating a cross section parallel with the 10 primary or transverse corrugations and at the valley thereof;

Figure '7 is an edge elevation of the piece of Figure 4 lookingalong the line. 1-1 of Figure 4 and simulating a cross section along a primary 15 or transverse corrugation at the ridge thereof;

Figure 8 is an edge elevation of the piece of Figure 4 looking along the line 8-8 of Figure 4 ll--Il of Figures 9 and 10, to show the relative 30 disposition of the air cells in the multi-cellular sheets and the third set of cells formed when two such sheets are internested as in Figures 9 and 10; and

Figure 12 is an edge elevation of another block of insulation wherein the internested or double cellular sheets are assembled in a difierent relation to build up the block.

Before describing theinsulating material in its completed form, I shall describe the method 40 and apparatus whereby it is produced and which constitutes the subject matter of the present application.

For the purpose of illustration, in Figure 1, which shows the apparatus, I have disregarded 45 proportions as to the insulating material itself, it being understood that the apparatus in practice will preferably be proportioned to produce the insulating material as shown in more accurate proportion in Figures 3 to 11, inclusive. 5

An upper paper sheet is is fed from a supply roll l6 by a friction faced feed wheel it. The under side of the sheet is coated with a thin film of latex from a spray ll. This may be latex as it comes from the rubber tree concentrated to a 55 one-third rubber content plus a preservative, if desired, but with rubber still in a colloidal form. The excess water content or surface moisture of the latex is largely absorbed by the uncoated craft paper. This absorbs water content and the remaining excess water content are evaporated by a drying roll l8 contacting the upper side of the sheet. 4

The sheet I5 is then engaged by a corrugating roll I! whose corrugations run longitudinally of the roll and transversely of the paper. For bringing the paper into the corrugations of the roll I9 I prefer suction rather than positive presure or a mating corrugated roll. For corrugating by suction, an air passage l-B' extends longitudinally of the corrugating roll l9 just radially inwardly from the bottom of each corrugation. A stationary arcuate plate 23 slidingly contacts each end face of the roll l3. It has a manifold-like channel 20' which at any moment engages the ends of the several passages l3 which correspond to the-corrugations which are at that time in contact with the paper.

At intervals cross ducts, 2| communicate between each passage I3' and the bottom-of the corresponding corrugation. Suction is applied to the corrugation bottoms by the cross ducts 2|, thepassages l3',the channels 20 and the suction pipes 20,". The bottoms and sides of each corrugation, the end plates 20, and the paper sheet I 5 combine to form a closed tubular chamber. This chamber being subjected to. suction, the paper is sucked up against the bottom of the corrugation. While the drying roll l6 has eliminated the surface moisture from the latex coating, the paper has been rendered moist and warm. The moist paper is better adapted for distortion by the corrugating roll. The melting point of rubber being about 248 F., the roll I8 should not be so hot as to subject the rubber film to that I high a temperature.

In the meantime, a second or backing sheet 22 has been fed from a supply 23, similarly sprayed with latex on its upper side by the spray 24, dried by the drying roll25, and brought over a platen roll 26 immediately beneath the corrugating roll l6.' The mating rolls 26 and I9 press the backing sheet 22 against the upper sheet l5 as it is corrugated, and the two are secured together by the adhesiveness of their latex coatings. The backing sheet 22 is fed by a friction faced feed roller 23' similar to the feed roller I6 for the upper sheet except the latter is larger in diameter. The rolls i6 and 26 together with the feed r'olls l6 and 23' may be driven synchronously and at the same R. P: M., the larger diameter of the feed roll l1 taking care of the additional length ,of paper required for the sheet I5 because of its being corrugated.

As the two-ply sheet is passed from the rolls l6 and 26, it consists of the backing sheet 22 untreated on its under side and latex coated on its upper side, and the corrugated upper sheet I5 su rposed thereon. The corrugated sheet is latex coated on its under side but not on its upper side. The outer sides of the two-ply sheet are thus non-sticky, and can be engaged by additional rolls for further operations without comper roll 28 is circumferentially beaded or ridged "at intervals as indicated at 30. The beads 30 of beads 33 than there are circumferential beads 30 on the roll 28. Preferably the number of beads 33 is a multiple of the number of beads 30 and preferably also certain of the beads 33 track the corrugations made by the beads 30.

, The reason for effecting the secondary or longitudinal corrugations in two steps and for the above mentioned relation between the beads 30 and 33 will presently be described.

As the two-ply sheet passes from the rollers 3i and 32, its top'is somewhat wailie-shaped or more precisely waille iron-shaped, while the back or under side is substantially flat. Both sides are then coated with latexby sprays 33 and 34,

whence they arepassed into along drying chamber 36. 7

As it emerges from the drying chamber the cellular sheet may be cut to convenient lengths, and then appears as illustrated in Figures 3 and 4 as supplemented by the cross sections of Figures 5,6,7 and 8.-

The lower sheet 22 is substantiallyfiat. The upper sheet I5 has primary or transverse corrugations 36 whose bottoms or valleys 36V are adhered to the back sheet 22 by the undercoating of latex rubber 31 on the sheet l5 and the upper coating 38 of latex rubber on the backing sheet 22. Superposed upon these transverse corrugations 36 are the secondary or longitudinal corrugations 33 giiiected by the beads 30 and 33 of the rolls 23 and Because the longitudinal comigations 39 are made subsequent to the transverse corrugations 36, the result is one of crushing down the transverse corrugations 36 at the-intersections 46 so that the cross section as seen in Figure 8, for example, is like that of a box pleat. The folds ll are the result of the upper sheet l5, being of greater length than the backing sheet 22. The top surface of the upper sheet l5 carries a coating of latex rubber 42, while the bottom of the back .by the transverse corrugations 36 and the backing sheet 22. If all of the longitudinal corrugations are formed simultaneously, the volume of each open-ended corrugation tube is decreased by increments as the-roll 3| passes over the corrugated sheet. Air within the tube displaced by this ensmalling of the volume passes out the ends. By the time the air cells 44 are sealed sothat no more air can pass out the ends of the corrugation, the ensmalling of the volume has been sub' stantially completed. The air trapped in the cells is at substantially atmospheric pressure at the moment. If the air has been'above room temperature as a result of heat transfer held over by the sheet from the drying roll l3, the air may soon contract slightly, putting the cell under slight suction. In either case the cell is not as resistant to collapsing as though air under slight pressure be trapped within it. It is chiefly for this reason that I prefer first to seal the ends of the primary corrugations 36 against the loss of air before subdividing the corrugations into the cells.

If I were to employ only the end beads 30 on the first longitudinal roll 28, it would meanthat all of the air thus sealed within the full volume of each tube formed by a transverse corrugation 36 would have to be distributed, as a result of the action of the roller 3|, among the several cells of the transverse corrugation. Because of the en-' smalling effect of the longitudinal corrugations 39 on the volume of the transverse corrugation tube, the aggregate volume of the air cells 44 in any transverse corrugation 36 is considerably less than the, original volume of the corrugation 36.

, As a result, the pressure would be dangerously increased in the respective-cells 44.

There is a practical limit to the internal air pressure for any individual cell 44. If it is too high the cell will be ruptured, most probably by tearing loose the seal afforded by the latex rubber adhesion. The maximum practical internal pressure for the cell is dependent on many factors, such as'the strength of the paper, the stickiness of the latex, the area of the seal as effected by the transverse and longitudinal corrugations, etc. By initially subdividing the transverse corrugations 36 into a plurality of sub-tubes 45 by the first longitudinal corrugating roll 28, I secure sealed subtubes whose internal pressure is substantially atmospheric pressure. This is because the subtubes 45 (Figure 1') are formed simultaneously and sealed by increments, so that the air displaced by the decreasing volume continues to pass out the end of the transverse corrugations 36 until the sub-tubes 45 are completely sealed.

Then by subdividing the sub-tubes 45 into still smaller divisions or cells 44, I can raise the inter- I find that when using-relatively light craftpaper and latex as described, where the primary or transverse corrugations run thirty-six to the foot, satisfactory results are obtained by placing the beads 30 on the first longitudinal corrugated roll 28 one and one-half inches apart and usingtwice as many annular beads 33 on the second corrugating roll 3| so that in the finished cellular sheet the longitudinal corrugations are threefourths of an inch apart.

It will be seen that my method and apparatus provide a very simple but effective solution to the problem of. corrugating and cross-corrugating a sheet and aifixing it to a bottom sheet, where both surfaces of both sheets are 'coated with a sticky material,-all without bringing any of the sticky coating material into contact with a roller. By the time that the finished sheet emerges from the drying chamber 35, the coating material is no longer so sticky but that it may be handled without difflculty. I Because the paper sheet to be corrugated is sucked pneumatically into the valleys between the teeth of the corrugating roll, instead of being pushed in by a mating corrugated roller, there is no danger of weakening or tearing the paper by squeezing it between metallic surfaces. It is also to be noted that the paper, as soon as it is corrugated, is immediately adhered to the backing sheet so that the pull of the feed rollers is preventedbythe flat backing sheet from pulling out or flattening the corrugations which have just been formed.

Using the multl-cellular sheet of Figure 3 as a unit, a plurality of such sheets may be assembled in anyone of a number of relations to build the desired over-all thickness. For greatest insulation value per inch of thickness of material, I prefer the assembly relation shown in Figure 9. In this the corrugated faces of two multi-cellular sheets are placed together in internesting relation. The primary or transverse corrugations 36 of the upper multi-cellular sheet'of a pair run parallel with those'of the lower multi-cellular sheet, but the sheets are offset longitudinally onehalf of the distance between corrugations 36 so that the ridges of the corrugations 36 on the upper sheet come in the valleys of the corrugations 36 of the lower sheet, and vice versa. The upper cellular sheet is also offset transversely relatively to the lower multi-cellular sheet by a distance equal to one-half of the. distance between the longitudinal corrugations 39, as shown in Figure 10. This results in a third set of transversely (I use the terms transverse and longibe no third set of cells formed. The third set of I cells 46 is formed as a result of the longitudinal corrugations 39 and in general the aggregate volume of the third set of cells 46 is equal to the aggregate volumetric decreasein the corrugations 36 resulting from the longitudinal corrugations 39. Thus while the use of the longitudinal corrugations 39 in subdividing the corrugations 36 reduces the aggregate cellular volume as far as the multi-cellular sheet itself is concerned, when two of these sheets are combined as illustrated in Figure 9, the lostvolume is replaced, taking theform of the third set of cells 46.

Asa matter of three dimensional geometry the outer conformations of the cells 44, when assembled as in Figure 9, will result in the third set of cells 46 being substantially non-communicating.

The coatings 42 of sticky rubber serve to compensate for any inaccuracies of the internestingfit and to seal the third set of cells 46 from one another. This seal may be made still more perfect by placing the internested pair of multi-cellular cells between two-parallel hot'sheets which are spaced apart a distance equal to the thickness of the pair of internested cellular sheets. The

heat of the plates will raise the temperature of the air trapped within the several cells and press their walls tightly together. This being done by internal pressure and not external pressure, there is no tendency to collapse the cells nor to lessen the thickness of the double sheet. It does, however, efiect a better adhesion between the mating surfaces of the upper and lower cellular sheets and thereby better insures that the third set of cells 46 is substantially sealed against intercommunication and hence against transmission of heat by convection currents of air.

' After the multi-cellular sheets have been internested in pairs to form double units, the double units have substantially flat exposed surfaces represented by the respective backing sheets 22. Two or more of these double units may be superposed as shown in Figure 9. A block may be built up to any desired thickness, the assembly being maintained by the adhesiveness of the rubber coatings 43 on the backing sheets 22.

In' Figure 11 I have shown another way of assembling the multi-cellular sheets of Figure 3.

tion in the refrigerator wall.

proximately the area of the desired section and the assembly indicated in Figures 9 and 10 may be made with multi-cel lular. sheets of that size.

When assembled to the desired thickness. the section may be trimmed as with a rotary knife. If desired, the section may be wrapped with plain or latex coated paper before being set into posi- If the assembly shown in Figures 9 and 10 be-used, it is unnecessary to seal the edges of the section, and the paper wrapping is not necessary. If the section is not to be wrapped the outer surfaces may be dusted with tale to facilitate handling.

I prefer, however, to spray with latex the entire exposed surface of a block of insulation material after the respective multi-cellular sheets have been assembled, but before it is wrapped if it is tobe wrap seal the block against the ingress or egress of moisture, air, gases, or odors even though there be unsealed interstices left especially between the backing plies of the multi-cellular sheets. I

I contemplate that materials other than latex may be used for the coatings herein described. I prefer to use latex for a number of reasons: It may be applied cold. It may be sprayed. The

rubber is not affected by heat under 248 F., making possible the use of steam heat in drying. This makes possible the use of my material in industrial insulating applications where temperatures would melt wax. compounds, for example. The

insulation will not be deteriorated even by coming in contact with live steam. The rubber coating being unvulcanized, I take advantage of the remarkable stability of unvulcanized rubber as against the action of time, moisture, light, heat (within the limit specified) and most gases. Unlike ,vulcanized rubber, it is odorless. It contains no sulphur or other ingredient which might affect metal parts with which it comes in contact. It not only coats the paper but to an extent impregnates the fibers. It is not conducive to mold or other fungus growths. The rubber is a good heat insulator. Its electrical insulating qualities make my insulation of advantage in heat insulating where poorly insulated electrical conductors are passed through it. v

The several latex coatings 31, 38, 42 and 43 are initially adhesive and retain their tackiness for at least several weeks. This permits the consummation of all assembly operations within a In this way I positively.

reasonable time while still having the advantage of the adhesive qualities of the rubber coating. In the course of time by incidental exposure the superficial surface of the coating will lose its tackiness, which is an advantage.- However, the rubber is not vulcanized and, therefore, will not deteriorate even on exposure to light.

While the rubber coating may be applied as a solution or as a calendered sheet, it is a feature of my invention that the rubber is applied as a spray or dip of latex wherein the rubber is in its natural colloidal suspension. This is more satisfactory and produces a better result than treating the paper with a form of rubber which has previously been chemically coagulated to separate it from the water content of the latex or where the rubber has previously been substantially dried.

While I have disclosed these specific embodiments of my invention, I contemplate that substitutions and changes may be made without departing from the scope of my invention. For

assembly, instead of starting with plain. sheets of paper and using the latex to adhere the corrugated sheet to. the base sheet, one may start with commercial corrugated paper consisting of a base sheet and a corrugated sheet adhered together by the conventional silicate of soda. This corrugated sheet and backing maybe dipped or otherwise coated with latex so that the inner surfaces of the tubes of the corrugations are treated, whereupon the longitudinal corrugations may be effected. The methods I have herein disclosed may be carried on more. largely as hand operations, if desired. Instead of a continuous manufacture, lengths of sheets may be fed by hand to the corrugators. Also, instead of using a backing sheet which is flat, I may use one which is corrugated like the top sheet, so that the two sheets or plies constituting the multi-cellular sheet are duplicates and arranged with their low regions adhered together.. In such case the cells are of substantially twice the volume and both sides of the multi-cellular sheet present corrugated surfaces which may be internested as previously described to build up blocks.

This application constitutes a division of my application, Serial No. 644,195, filed November 25,

1932, on Insulating material.

I claim: 1. The method of fabricating an insulating material which consists in coating the under side of a top sheet of paper and the upper side of a bottom sheet of paper with adhesive rubber, corrugating one of the sheets, and adhering the corrugated sheet to the other or backing sheet by the adheslveness of the ,rubber coatings.

2. The method of fabricating an insulating material which consists in coating the under side of a top sheet of paper and the upper side of a bottom sheet of paper with adhesive rubber, corrugating one of the sheets, adhering the corrugated sheet to the other or backing sheet by the adheslveness of the rubber coatings, and then subdividing the corrugations by imposing corrugations transversely thereon to form a multiplicity of shorter cells.

material which consists in coating the under side of a top sheet of paper and the upper side of a bottom sheet of paper with adhesive waterproof material, corrugating one of the sheets, adhering the corrugated sheet to the other or backing sheet stantially atmospheric 'pressure,and then further gation-to the coated side of a second sheet of paper, subsequently impressing secondary cross subdividing the sub-tubes-into sealed air cells of lesser aggregate volume than the tubes whereby the internal air pressure of the cells is. above atmospheric pressure.

6. The method of fabricating insulating material, which consists in coating with an adhesive the inner. side of a first sheet of paper, then corrugating the, first sheet of paper by pneumatically sucking'the paper against a corrugationdefining roller with the coated side of the sheet away from the roller, then adhering the edges of the corrugation to the coated side-of a second sheet of paper.

7. The method of fabricating insulating material, which consists in coating with an adhesive the inner side of a first sheet of paper, then corrugating the first sheet of paper by pneumatically sucking the paperagainst a corrugation-defining roller with the coated side of the sheet away fromthe roller, then adhering the edges of the corrugation to the coated side of a second sheet of paper, and subsequently impressing secondary cross-corrugations upon the primary corrugations.

8. The method of fabricating insulating material, which consists in coating with an adhesive the inner side of a first sheet of paper, then corrugating the first sheet of paper by pneumatically sucking the paper against a corrugation-defining roller with the coated side of the sheet away from the roller, then adhering the edges of the corrucorrugations upon the primary corrugations, and thereafter coatingv the outside surfaces of the combined sheets.

9. The method of corrugating a sheet of paper which'consists in passing it over a roller having longitudinally extending peripheral corrugations andpneumatically sucking the paper into the corrugations. t

10. The method of corrugating paper, which consists in passing the paper over a roller having longitudinally arranged peripheral corrugations and applying suction to the bases only of the corrugations pneumatically to suck the paper thereinto. t

'11. The method of fabricating an insulating material, which consists in pneumatically suck- .ing a sheet of paper into corrugations in a corrugation-defining die and while the paper is pneumatically held therein in corrugated position, adhering thereto a backing Sheet.

12. The method of progressively fabricating insulating material from two separately rolled sheets of paper, which consists in spraying an adhesive coating simultaneously on the under side of the top sheet and the top side of the bottom sheet, passing the combined sheets between mating rolls one of which is longitudinally corrugated on its periphery, pneumatically sucking the top sheet, with its coated side outermost, into the corrugations to define corrugations in the top sheet, and while the paper is held'in such corrugated position adhering the bottom sheet thereto as a backing sheet by the adhesion of the coatings by pressure between the rolls.

' 13. The method of progressively fabricating insulating material from two separately rolled sheets of paper, which consists in spraying an adhesive coating simultaneously on the under side of the top sheet and the top side of the bottom sheet, passing the combined sheets between mating rolls one of which is longitudinally corrugated on its periphery, pneumatically sucking the top sheet, with its coated side outermost, into the corrugations to define corrugations in the top sheet, and while the paper is held in such corrugated position adhering the bottom sheet there'- to as a backing sheet by the adhesion of the coatings by pressure between the rolls, and subsequently superposing secondary corrugations at an angle to the first mentioned corrugations.

14. An apparatus for fabricating sheet paper insulating material comprising a feed mechafirst corrugations, and means .for coating the outersurfaces of the sheets.

15. An apparatus for transversely corrugating a sheet of paper, which comprises a. roll having longitudinally arranged peripheral corrugations, passage means in the roll for applying suction to the bases of the corrugations pneumatically to suck the paper into the corrugations, and means for feeding the paper over the roll.

16. An apparatus for fabricating paper sheets, comprising asupport for a first roll of paper and a support for a second roll of paper, a pair of primary mating rollers one of which has longitudinally arranged peripheral corrugations, means for feeding thepaper from the respective rolls'into overlapping relationship between the primary rolls, means for spraying an adhesive coating onto the under side of the upper sheet and the upper side of the lower sheet before they pass between the primary rolls, air passage means within the corrugated roll for pneumatically O sucking the top sheet, before it comes into contact with the lower sheet, into the corrugations to form corrugations in the upper sheet, the other of the primary rolls pressing the lower sheet into adhesive contact with the corruga- 68 a support for a second roll of paper, a pair of 70 primary mating rollers one of which has longitudinally arranged peripheral corrugations, means for feeding the paper from the respective rolls into overlapping relationship between the primary rolls, means for spraying an adhesive coating onto the under side of the upper sheet and the upper side of the lower sheet before they pass between the primary rolls, air passage means within the corrugated roll; for pneumatically sucking the top sheet, before it comes into contact with the lower sheet, into the corrugations to form corrugations in the upper sheet, the other of the primary rolls pressing the lower sheet into adhesive contact with the corrugations of the upper sheet while held in the corrugated roll, and a posteriorly disposed pair of secondary rollers, the upper of which is circumferentially corrugated, and between which rolls the adhered corrugated and lower sheets pass for imposing secondary corrugations upon the corrugated sheet.

18. An apparatus for fabricating paper sheets, comprising a support for a first roll of paper and a support for a second roll of paper, a pair of primary mating rollers one of which has longitudinally arranged peripheral corrugations, means for feeding the paper from the respective rolls into overlapping relationship between the primary rolls, means for spraying an adhesive coating onto the under side of the upper sheet and the upper side of the lower sheet before they pass between the primary rolls, air passage means within the corrugated roll for pneumatically sucking the top sheet, before it comes into contact with the lower sheet, into the corrugations to form corrugations in the upper sheet, the other of the primary rolls pressing the lower sheet into adhesive contact with the corrugations of the upper sheet while held in the corrugated roll, a posteriorlydisposed pair of secondary rollers, the upper of which is circumferentially corrugated, and between which rolls the adhered corrugated and lower sheets pass for imposing secondary corrugations upon the corrugated sheet, and means for applying coating to the top side of the corrugated sheet and the bottom side of the backing sheet after the sheets have passed between the primary and secondary rolls.

. JOHN F. PALMER. 

